Polarization Measurements and Analysis inn−He4Scattering from 11.0 to 30.3 MeV

Measurements of the polarization function $P\left(\theta \right)$ in $n-{}_{}{}^4{}_{}{}^{}\mathrm{He}$ scattering have been made at neutron energies of 11.0, 17.7, 23.8, 25.7, 27.3, and 30.3 MeV with the aim of improving upon previous descriptions of the interaction, especially as regards the analyzing power. Significant differences were found at the higher energies between experimental values for $P\left(\theta \right)$ and predictions of previously existing $n-{}_{}{}^4{}_{}{}^{}\mathrm{He}$ scattering phase shifts. The new polarization data were used with published $n-{}_{}{}^4{}_{}{}^{}\mathrm{He}$ cross-section and polarization data in a series of single-energy phase-shift searches in an attempt to provide an improved set of phase shifts above 20 MeV.